Field of the Invention
The present disclosure relates to a voltmeter for measuring the peak voltage of a high voltage pulse applied to an electric fence. More particularly, the present disclosure relates to an electric fence voltmeter having a peak detection type voltage divider that provides positive and negative peak voltages with an additional pulse state voltage. The voltmeter is extremely simple in configuration, but is able to measure the peak voltage accurately in a reliable and efficient manner using the pulse state voltage that has information on the moments the high voltage pulse starts and peaks.
Related Art
An electric fence prevents the intrusion of wild animals, or the escape of livestock cultivated in the fence. A pulse shaped high voltage generated from an energizer is applied between the ground (earth) and the fence wire which is supported by the insulators installed around fence posts. If an animal is in contact with the fence wire, a strong pain is caused by an electric shock due to the circulating current flowing through the animal.
Most of the electric fence energizer has a transformer that has more turns on the secondary winding than the primary to induce a high voltage pulse having a peak value of 2 kV to 10 kV. The high voltage pulse is induced from the secondary winding of the transformer when the electric charge stored in an energy storage capacitor is discharged through the primary winding. The reason for raising the fence voltage up to 10 kV is to breakdown the electrical insulating effect that the animal hairs have.
The period of applying high voltage pulses to the electric fence wire is usually 0.75 to 1.5 seconds, and the pulse duration is 5 to 500 microseconds. The high voltage pulses have normally positive polarity relative to the ground, but may also have a negative polarity.
Sometimes, the electric fence experiences unwanted low voltage on the fence wire due to the various reasons including the failure of the electric fence energizer itself, the fence wire in contact with trees or weeds, the broken or sagging fence wire on the ground, and the broken insulators.
Once the fence voltage is lowered, the current flowing through the animal becomes weak or may not flow at all. Thus, in order to maintain the electric fence effectively, the voltage applied to the fence wire must be measured frequently by using an adequate voltmeter to ensure that a predetermined high voltage is applied.
In U.S. Pat. No. 2,450,153 A, issued to S. A. Moore, on Sep. 28, 1948, the patent discloses a voltage indicator for electric fences. In the voltage indicator, the fence voltage to be tested is applied to a plurality of resistors which are connected in series to form a voltage dividers, and each resistor has a neon bulb connected in parallel. Consequently, by properly choosing the resistances, it is possible to light a plurality of bulbs selectively corresponding to the strength of the test voltage. This type of device indicates the voltage very roughly, but it is still used when the exact voltage reading is not important.
Detailed discussion on recent technologies is provided in “The design of an electric fence fault finder”, M. Sc. Thesis, Massey University New Zealand by Glen McGillan (2009), pp 37-98. The article describes a detailed design of the modern peak voltage detecting circuits. The voltage measuring circuits are based on a resistor voltage divider of which the output is fed to the separated two peak detector circuits to provide the peak voltages of both positive and negative pulses. The peak voltages are read by A/D (analog to digital) conversion channels of an MCU (micro controller unit) and displayed on a display unit.
Most of known modern electric fence voltmeters are concerned that they have too complicated configuration including buffers, inverting amplifiers, and peak detectors, so on. Besides, they also have a problem with determining the time that the pulse reaches its peak.
For the foregoing reasons, there is a need for a simple cost-effective electric fence voltmeter that measures accurately, while draws less power from a battery.